1. Field of the Invention
This invention relates to a power steering including a flow control valve for controlling a flow introduced toward a power cylinder.
2. Description of Related Art
A flow control valve installed in this type of power steering has a spool which is mounted inside a main body and has one end facing one of pilot chambers which is communicated with a pump port at all times and the other end facing the other pilot chamber incorporating a spring. A fixed orifice is formed downstream from the other pilot chamber. Pressure oil is introduced through the fixed orifice into a steering valve for controlling a power cylinder.
On the other hand, movement positions of the spool is controlled with pressure balance between both pilot chambers wherein pressure upstream from the orifice is set as pilot pressure of the one pilot chamber and pressure downstream from there is set as pilot pressure of the other pilot chamber.
It is configured to use the movement position of the spool for distribution of the pressure oil between a control flow rate QP of the flow for introducing the amount of discharge from a pump into the steering valve and a return flow rate QT for making the flow circulation-return toward a tank or a pump.
The above spool is designed to be maintained in a constant state of differential pressure after and before the fixed orifice, to supply a constant control flow rate QP to the steering valve for controlling the power cylinder at all times.
In such conventional power steering, a constant control flow rate QP is supplied from the flow control valve to the steering valve for controlling the power cylinder at all times. In other words, regardless of vehicle speed or steering conditions, the control flow rate QP is continuously supplied to the steering valve at a constant control flow rate QP at all times.
However, if the control flow rate QP is defined regardless of the vehicle speed or a steering status, for example, when a relation of QP with respect to the flow rate QM required by the power cylinder becomes QP greater than QM, the need for returning the resulting surplus flow rate to a tank through the above steering valve arises.
As described above, returning the surplus flow rate to the tank through the steering valve results in increase of a pressure loss in the circuit. Put another way, the pump is required to continue consuming the driving torque to make up for the amount of pressure loss. Therefore, as driving torque increases, energy consumption increases.
Moreover, since the control flow rate QP is set in accordance with the maximum required flow rate for the power cylinder, under present circumstance, some surplus flow rate is often returned to the tank. Thus, the conventional system has a problem associated with increase of energy consumption.
It is an object of the present invention to provide a power steering which is capable of reducing an energy loss to a minimum by controlling a control flow rate QP as travelling conditions or a steering status of a vehicle.
The present invention is predicated on configuration in which: a spool is mounted in a main body and has one of ends facing one of pilot chambers which communicates with a pump port at all times and the other end facing the other pilot chamber incorporating a spring. An orifice is provided downstream from the one pilot chamber. Pressure oil is introduced through the orifice into a steering valve for controlling a power cylinder. A movement position of the spool is controlled with a pressure balance between both the pilot chambers when pressure upstream from the orifice is set as a pilot pressure of the one pilot chamber and pressure downstream from the orifice is set as a pilot pressure of the other pilot chamber. The pressure oil is distributed between a control flow rate QP for introducing the amount of discharge from a pump toward the steering valve, and a return flow rate QT for making the pressure oil circulation-return toward a tank or the pump.
Based on the above power steering, a first invention features as follows: the orifice is a variable orifice controlling the degree of its opening in accordance with an excitation current of a solenoid. Also, a controller is provided for controlling the excitation current of the solenoid for the variable orifice. The controller is connected with a steering torque sensor, and calculates or stores a solenoid current instruction value IT in response to a steering torque signal from the steering torque sensor. Further, a solenoid current instruction value IS for standby is added to the solenoid current instruction value IT. Then the excitation current I of the solenoid SOL for the variable orifice is controlled based on the added instruction value.
According to the power steering of the first invention, the control flow rate QP can be controlled by means of detecting the steering torque. Therefore, the control flow rate QP is appropriately secured to accomplish an energy-saving type control.
Also, when the steering wheel is held stationary, the control flow rate QP can be appropriately secured by means of the steering torque thereby to allow the vehicle to resist a self-aligning torque.
Further, the standby flow rate can be secured even when the solenoid current instruction value IT based on the steering torque is zero, for example, in travel of the vehicle in a straight line. Therefore, the power steering can be prevented from seizure, and is capable of handling disturbances caused by a kick back or the like, and further sufficient response can be ensured.
In any of times when the steering wheel is turned, when the steering wheel is held stationary, and when the vehicle travels in a straight line, the control flow rate QP is appropriately secured not to increase torque for driving the pump P more than necessary thereby to attain the accurate energy-saving control.
In the power steering, a signal of the steering torque, the vehicle speed or the like has been conventionally used for controlling a steering reaction force on the output side or controlling sensitivity of the steering valve. However, the present invention has been made under the theme of energy savings and therefore uses a signal of the steering torque, the vehicle speed or the like to control the control flow rate QP, which has not been seen in prior art.
Moreover, in the present invention, the steering torque is directly detected thereby to obtain a more accurate value without need of other sensors or calculating means.
The present invention approaches the subject of energy savings and has the principal feature in that a signal of the steering torque, the vehicle speed or the like is used.
A second invention has configuration in which the controller is connected to a vehicle speed sensor, and calculates or stores a solenoid current instruction value IV in response to a vehicle speed signal from the vehicle speed sensor, while multiplying the solenoid current instruction value IT by the solenoid current instruction value IV, and adding the solenoid current instruction value IS for standby to the multiplied value.
A third invention has configuration in which the controller is connected to a vehicle speed sensor, and calculates or stores a solenoid current instruction value IV in response to a vehicle speed signal from the vehicle speed sensor, while setting the solenoid current instruction value IV in response to the vehicle speed signal as a threshold value based on the solenoid current instruction value IT, and adding a solenoid current instruction value under the set threshold value to the solenoid current instruction value (TS) for standby.
A fourth invention has configuration in which the controller multiplies characteristics of the excitation current I of the solenoid and the control flow rate QP determined by the degree of opening of the variable orifice, and characteristics of the steering torque and the solenoid current instruction value IT together, to allow the steering torque and the control flow rate QP, which is determined by the degree of opening of the variable orifice in accordance with the solenoid current IT, to have linear characteristics.
According to the power steering of the second invention, since the power steering is designed in a speed sensitive type, the energy-saving type control in accordance with the vehicle speed is allowed.
According to the power steering of the third invention, it is designed in a vehicle-speed sensitive type, but the solenoid current instruction value IV based on the vehicle speed is used as a limiter, resulting in maintaining further sufficient response.
According to the power steering of the fourth invention, since the control flow rate QP with respect to the steering torque is permitted to have further linear characteristics, a driver""s steering feel is improved.
Based on the aforementioned power steering, a fifth invention features as follows: the orifice is a variable orifice controlling the degree of its opening in accordance with an excitation current I of a solenoid. Also, a controller is provided for controlling the excitation current I of the solenoid for the variable orifice. The controller is connected with a steering angle sensor, to store or calculate a steering angle xcex8 and a steering angular velocity xcfx89 in accordance with a steering angle from the steering angle sensor, while calculating or storing a solenoid current instruction value I0 in accordance with the steering angle xcex8 and a solenoid current instruction value I107  in accordance with the steering angular velocity xcfx89, and adding the solenoid current instruction values Ixcex8 and Ixcfx89, and further adding the added value to a solenoid current instruction value IS for standby, and then controlling the excitation current I of the solenoid for the variable orifice based on the finally added instruction value.
A sixth invention has configuration in which the controller is connected to a vehicle speed sensor, and calculates or stores a solenoid current instruction value IV in response to a vehicle speed signal from the vehicle speed sensor, while multiplying the added value of the solenoid current instruction values Txcex8 and Ixcfx89 by the solenoid current instruction value IV, and adding the solenoid current instruction value IS for standby to the multiplied value.
A seventh invention has configuration in which the controller is connected to a vehicle speed sensor, and calculates or stores a solenoid current instruction value IV in response to a vehicle speed signal from the vehicle speed sensor, while setting the solenoid current instruction value IV based on the vehicle speed signal as a threshold value with respect to the added value of the solenoid current instruction values I0, and Ixcfx89, and adding a solenoid current instruction value under the set threshold value to the solenoid current instruction value IS for standby.
Based on the aforementioned power steering, a eighth invention features as follows: the orifice is a variable orifice controlling the degree of its opening in accordance with an excitation current I of a solenoid. Also, a controller is provided for controlling the excitation current I of the solenoid for the variable orifice. The controller is connected with a steering angle sensor to calculate or store a steering angle xcex8 and a steering angular velocity xcfx89 in accordance with a steering angle from the steering angle sensor, while storing or calculating a solenoid current instruction value Ixcex8 in accordance with the steering angle xcex8 and a solenoid current instruction value Ixcfx89 in accordance with the steering angular velocity xcfx89, and selecting any larger solenoid current instruction value from the solenoid current instruction values Ixcex8 and Ixcfx89, and adding a solenoid current instruction value IS for standby to the selected value, and then controlling the excitation current I of the solenoid for the variable orifice based on the finally added instruction value.
According to the power steering of the fifth and eighth inventions, the steering angular velocity xcfx89 is detected thereby to control the control flow rate QP at a value closer to that of the steering torque. Therefore, it is possible to appropriately secure the control flow rate QP to achieve the energy-saving type control.
When the steering wheel is held stationary, the control flow rate QP is appropriately secured by means of the steering angle xcex8, to allow the vehicle to resist the self-aligning torque.
Further, for example, in the vehicle travelling in a straight line, even when the solenoid current instruction value Ixcex8 based on the steering angle xcex8 or the solenoid current instruction value Ixcfx89 based on the steering angular velocity xcfx89 is zero, the standby flow rate can be secured. Therefore, the power steering can be prevented from seizure, and is capable of handling disturbances caused by a kick back or the like, and further sufficient response can be ensured.
In any of times when the steering wheel is turned, when the steering wheel is held stationary, and when the vehicle travels in a straight line, the control flow rate QP is appropriately secured not to increase the torque for driving the pump P more than necessary, resulting in making the correct energy-saving control implementable.
In the power steering, a signal of the steering angle, the steering angular velocity, the vehicle speed or the like has been conventionally used for controlling a steering reaction force on the output side or controlling sensitivity of the steering valve. However, the present invention has been made under the theme of energy savings and therefore uses a signal of the steering angle, the steering angular velocity, the vehicle speed or the like to control the control flow rate QP, which has not been seen in prior art.
The present invention approaches the subject of energy savings and has the principal feature in that a signal of the steering angle, the steering angular velocity, the vehicle speed or the like is used.
A ninth invention has configuration in which the controller is connected to a vehicle speed sensor, and calculates or stores a solenoid current instruction value IV in response to a vehicle speed signal from the vehicle speed sensor, while multiplying the any larger value of the solenoid current instruction values I0 and Ixcfx89 by the solenoid current instruction value IV, and adding the multiplied value to the solenoid current instruction value IS.
According to the power steering of the sixth and ninth inventions, since the power steering is designed in a speed sensitive type, the energy-saving type control in accordance with the vehicle speed is allowed.
A tenth invention has configuration in which the controller is connected to a vehicle speed sensor, and calculates or stores a solenoid current instruction value IV in response to a vehicle speed signal from the vehicle speed sensor, while setting the solenoid current instruction value IV based on the vehicle speed signal as a threshold value with respect to the any larger value of the solenoid current instruction values Ixcex8 and Ixcfx89, and adding a solenoid current instruction value under the set threshold value to the solenoid current instruction value IS.
According to the power steering of the seventh and tenth inventions, it is designed in a vehicle-speed sensitive type, but the solenoid current instruction value IV based on the vehicle speed is used as a limiter, resulting in maintaining further sufficient response.
A eleventh invention has configuration in which the controller multiplies characteristics of the excitation current I of the solenoid and the control flow rate QP determined by the degree of opening of the variable orifice, and characteristics of the steering angle xcex8 and the solenoid current instruction value I0 together, to allow the steering angle xcex8 and the control flow rate QP determined by the degree of opening of the variable orifice in accordance with a solenoid current I1 to have linear characteristics.
A twelfth invention has configuration in which the controller multiplies characteristics of the excitation current I of the solenoid and the control flow rate QP determined by the degree of opening of the variable orifice, and characteristics of the steering angular velocity xcfx89 and the solenoid current instruction value I2 together, to allow the steering angular velocity xcfx89 and the control flow rate QP determined by the degree of opening of the variable orifice in accordance with a solenoid current Ixcfx89 to have linear characteristics.
According to the power steering of the eleventh and twelfth inventions, since the control flow rate QP with respect to the steering angle is permitted to have further linear characteristics, a driver""s steering feel can be improved.
Based on the aforementioned power steering, a thirteenth invention features as follows: the orifice is a variable orifice controlling the degree of its opening in accordance with an excitation current I of a solenoid. Also a controller is provided for controlling the excitation current I of the solenoid for the variable orifice. The controller is connected with a steering angle sensor, to calculate or store a steering angle xcex8 and a steering angular velocity xcfx89 in accordance with a steering angle from the steering angle sensor, while the controller storing or calculating a solenoid current instruction value Ixcex8 in accordance with the steering angle xcex8 and a solenoid current instruction value Ixcfx89 in accordance with the steering angular velocity xcfx89, and multiplying the solenoid current instruction value Ixcex8 in accordance with the steering angle xcex8 and a steering-angle current instruction value IV1 in accordance with the vehicle speed together, while the current instruction values Ixcfx89 in accordance with the steering angular velocity xcfx89 being imparted with a threshold value defined by a steering-angular-velocity current instruction value IV2 in response to the vehicle speed signal, and it being determined which of the multiplied value I1 of the solenoid current instruction values Ixcex8 and IV1 and the solenoid current I2 including the steering-angular-velocity current instruction value IV2 as the threshold value is larger, to control the excitation current I of the solenoid for the variable orifice based on the larger value.
According to the thirteenth invention, since the solenoid excitation current I is determined with reference to the steering angle in high-speed travel, the safety of the steering can be ensured.
Also, since the solenoid excitation current I is determined with reference to the steering angular velocity in low-speed travel, the safety of the steering can be ensured.
Additionally, even in high-speed travel, it is possible to ensure the response within the range of the threshold value referred to the vehicle speed when the steering wheel is sharply and abruptly operated. This further improves the safety under the circumstances where the vehicle is steered around an obstacle during high-speed travel, and the like.
Also, when the steering wheel is held stationary, the control flow rate QP is properly secured by means of the steering angle xcex8, to allow the vehicle to resist the self-aligning torque.
A fourteenth invention has configuration in which the larger current instruction value is added to a solenoid current instruction value IS for standby.
According to the fourteenth invention, it is possible to secure the standby flow rate even when the steering angle xcex8 or the steering angular velocity xcfx89 is zero, for example, in travel of the vehicle in a straight line. Therefore, the power steering can be prevented from seizure, and is capable of handling disturbances caused by a kick back or the like, and further sufficient response can be ensured.
In either of the thirteenth invention or the fourteenth invention, in any of times when the steering wheel is turned, when the steering wheel is held stationary, and when the vehicle travels in a straight line, the control flow rate QP is appropriately secured not to increase the torque for driving the pump P more than necessary. This makes the correct energy-saving control implementable.
In the power steering, a signal of the steering angle, the steering angular velocity, the vehicle speed or the like has been conventionally used for controlling a steering reaction force on the output side or controlling sensitivity of the steering valve. However, the present invention has been made under the theme of energy savings and therefore uses a signal of the steering angle, the steering angular velocity, the vehicle speed or the like to control the control flow rate QP, which has not been seen in prior art.
The present invention approaches the subject of energy savings and has the principal feature in that a signal of the steering angle, the steering angular velocity, the vehicle speed or the like is used.